WO2014092110A1 - 光ファイバ製造方法および光ファイバ - Google Patents

光ファイバ製造方法および光ファイバ Download PDF

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Publication number
WO2014092110A1
WO2014092110A1 PCT/JP2013/083169 JP2013083169W WO2014092110A1 WO 2014092110 A1 WO2014092110 A1 WO 2014092110A1 JP 2013083169 W JP2013083169 W JP 2013083169W WO 2014092110 A1 WO2014092110 A1 WO 2014092110A1
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Prior art keywords
optical fiber
transmission loss
wavelength
heating furnace
less
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PCT/JP2013/083169
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English (en)
French (fr)
Japanese (ja)
Inventor
春名　徹也
平野　正晃
欣章 田村
中西　哲也
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住友電気工業株式会社
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Application filed by 住友電気工業株式会社 filed Critical 住友電気工業株式会社
Priority to EP13861713.9A priority Critical patent/EP2933240B1/de
Priority to US14/651,483 priority patent/US9527765B2/en
Priority to CN201380064885.5A priority patent/CN104854047B/zh
Publication of WO2014092110A1 publication Critical patent/WO2014092110A1/ja
Priority to US15/351,782 priority patent/US9932265B2/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C13/00—Fibre or filament compositions
    • C03C13/04—Fibre optics, e.g. core and clad fibre compositions
    • C03C13/045—Silica-containing oxide glass compositions
    • C03C13/046—Multicomponent glass compositions
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
    • C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
    • C03B37/027—Fibres composed of different sorts of glass, e.g. glass optical fibres
    • C03B37/02718—Thermal treatment of the fibre during the drawing process, e.g. cooling
    • C03B37/02727—Annealing or re-heating
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C13/00—Fibre or filament compositions
    • C03C13/04—Fibre optics, e.g. core and clad fibre compositions
    • C03C13/045—Silica-containing oxide glass compositions
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02395—Glass optical fibre with a protective coating, e.g. two layer polymer coating deposited directly on a silica cladding surface during fibre manufacture
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
    • C03B2201/50—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with alkali metals
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2205/00—Fibre drawing or extruding details
    • C03B2205/55—Cooling or annealing the drawn fibre prior to coating using a series of coolers or heaters
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2205/00—Fibre drawing or extruding details
    • C03B2205/56—Annealing or re-heating the drawn fibre prior to coating
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/21—Doped silica-based glasses containing non-metals other than boron or halide containing molecular hydrogen
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/30—Doped silica-based glasses containing metals
    • C03C2201/50—Doped silica-based glasses containing metals containing alkali metals
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/50—After-treatment
    • C03C2203/52—Heat-treatment
    • C03C2203/54—Heat-treatment in a dopant containing atmosphere
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
    • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

  • the present invention relates to an optical fiber manufacturing method and an optical fiber.
  • An optical fiber having a core made of silica glass containing GeO 2 as an additive for increasing the refractive index is referred to as “GeO 2 -doped core light”. It is called “fiber”.
  • An optical fiber having a core made of substantially pure silica glass that does not contain an additive for increasing the refractive index (GeO 2 , Al 2 O 3, etc.) is referred to herein as a “pure silica core optical fiber”. Pure silica core optical fiber has low transmission loss compared to GeO 2 -doped core optical fiber and is said to have good long-term reliability such as hydrogen resistance and radiation resistance (Y.
  • the GeO 2 -doped core optical fiber may be exposed to deuterium gas (D 2 ) under certain conditions for the purpose of improving hydrogen resistance (see JP2003-261351A).
  • D 2 deuterium gas
  • pure silica core optical fibers have good hydrogen resistance, so that exposure to deuterium gas is generally not necessary.
  • a heating furnace is installed in the vicinity of the outlet of the drawing furnace, and the optical fiber immediately after drawing is passed through the heating furnace.
  • the optical fiber is heated to be within a predetermined temperature range. In this way, the optical fiber immediately after drawing is reheated by the heating furnace, so that rapid cooling of the optical fiber after drawing is prevented and gradually cooled.
  • the heating furnace is lengthened to several tens of meters or a drawing speed ( It is necessary to further promote the relaxation of the glass network structure by reducing the speed of the optical fiber drawn from the drawing furnace to several tens of m / min.
  • the productivity is remarkably deteriorated.
  • alkali metal doped optical fiber is known as an optical fiber that can reduce Rayleigh scattering intensity (JP2005-537210A, US2006 / 0130530A, JP2007-504080A, JP2008-536190A, JP2010-501894A, JP2009-541796A, JP2010). -526749A, WO98 / 002389, see US5146534B).
  • An alkali metal-doped optical fiber is a core made of silica glass containing a trace amount of an alkali metal (for example, Na, potassium, etc.) of 500 ppm or less without containing an additive for increasing the refractive index such as GeO 2 or Al 2 O 3. It means the optical fiber.
  • the viscosity of the core portion can be lowered when the optical fiber preform is drawn, and the relaxation of the silica glass network structure proceeds. For this reason, it is said that the fictive temperature Tf in the optical fiber is lowered and transmission loss can be reduced.
  • the core of the alkali metal-doped optical fiber has a small amount of not only the amount of alkali metal added but also the amount of halogen such as Cl and fluorine.
  • An object of the present invention is to provide a low-loss alkali metal-doped optical fiber having excellent hydrogen resistance characteristics and a method capable of manufacturing such an optical fiber.
  • an optical fiber preform is drawn in a drawing furnace to form a silica glass system having a core region containing an alkali metal having an average concentration of 0.5 atomic ppm or more and a cladding region surrounding the core region.
  • an optical fiber manufacturing method including a drawing step of manufacturing an optical fiber and a heating step of heating the optical fiber in a heating furnace through which the optical fiber drawn from the drawing furnace passes.
  • the temperature in the heating furnace in the heating step may be 700 ° C. or higher, 1000 ° C. or higher, and 1000 ° C. or higher and 1500 ° C. or lower.
  • the residence time of the optical fiber in the heating furnace may be 0.2 seconds or more, or 0.2 seconds or more and 2 seconds or less.
  • the product of the residence time of the optical fiber in the heating furnace and the average temperature in the heating furnace in the heating step may be 480 (second ⁇ ° C.) or more.
  • the drawing speed may be 150 m / min or more, or 150 m / min or more and 1000 m / min or less.
  • the alkali metal may be potassium.
  • a silica glass-based optical fiber having a core region containing an alkali metal having an average concentration of 0.5 atomic ppm or more and a cladding region surrounding the core region, the transmission loss at a wavelength of 1550 nm.
  • an optical fiber having a transmission loss at a wavelength of 1550 nm of 0.003 dB / km or less by exposure to a hydrogen atmosphere having a partial pressure of 1 kPa for 720 hours at a temperature of 25 ° C. of 0.158 dB / km or less.
  • a silica glass optical fiber having a core region containing an alkali metal having an average concentration of 0.5 atomic ppm or more and a cladding region surrounding the core region, and having a transmission loss of 0.158 dB / km at a wavelength of 1550 nm.
  • an optical fiber having an increase in transmission loss at a wavelength of 1560 nm to 1620 nm by exposure to a hydrogen atmosphere having a partial pressure of 1 kPa for 720 hours at a temperature of 25 ° C. of 0.005 dB / km or less.
  • silica glass-based optical fiber having a core region containing an alkali metal having an average concentration of 0.5 atomic ppm or more and a cladding region surrounding the core region, and has a transmission loss of 0.158 dB / km at a wavelength of 1550 nm.
  • An optical fiber after being exposed to a deuterium atmosphere having a partial pressure of 2 kPa at a temperature of 40 ° C. for 24 hours and having a wavelength of 1550 nm by being exposed to a hydrogen atmosphere having a partial pressure of 1 kPa at a temperature of 25 ° C. for 720 hours.
  • An optical fiber having an increase in transmission loss at 0.002 dB / km or less is provided.
  • silica glass-based optical fiber having a core region containing an alkali metal having an average concentration of 0.5 atomic ppm or more and a cladding region surrounding the core region, and the transmission loss at a wavelength of 1550 nm is 0.158 dB /
  • An optical fiber after being exposed to a deuterium atmosphere having a partial pressure of 2 kPa at a temperature of 40 ° C. for 24 hours at a temperature of 40 km or less, and being exposed to a hydrogen atmosphere having a partial pressure of 1 kPa at a temperature of 720 hours at a temperature of 25 ° C.
  • An optical fiber having an increase in transmission loss at 1560 nm to 1620 nm of 0.003 dB / km or less is provided.
  • FIG. 6 is a chart summarizing various manufacturing conditions and characteristics of an optical fiber of a comparative example.
  • the silica glass network containing the alkali metal is likely to be cut, and point defects such as non-crosslinked oxygen centers are likely to occur. Therefore, according to the knowledge of the present inventor, the alkali metal-doped optical fiber may be deteriorated in hydrogen resistance characteristics as compared with a pure silica core optical fiber.
  • the hydrogen resistance property represents the stability of the transmission loss of the optical fiber against hydrogen molecules, and is one of the long-term reliability items of the optical fiber.
  • the hydrogen gas generated from the coating material around the glass part and the metal in the optical fiber cable gradually permeates and reacts with the glass part of the optical fiber, and reacts with OH.
  • a base defect or a point defect occurs, and transmission loss increases. Therefore, as an accelerated test, by investigating the dependence on the temperature, hydrogen partial pressure, and time of the reactivity of the manufactured optical fiber with hydrogen, the reaction with hydrogen in the service life of the optical fiber is used. It is known that an increase in transmission loss can be estimated.
  • the present inventor has further found that, in the alkali metal-doped optical fiber, a new increase in transmission loss that gradually increases from the wavelength 1500 nm band to the long wavelength side occurs due to hydrogen treatment.
  • the alkali metal-doped optical fiber has a problem that hydrogen resistance, which is one of long-term reliability, may deteriorate.
  • increasing the alkali metal concentration promotes relaxation of the glass network structure and reduces Rayleigh scattering loss, but on the other hand, structural irregularities in the glass increase. Further, there is a problem that an increase in transmission loss independent of wavelength may occur.
  • the optical fiber manufacturing method of the present invention includes a base material manufacturing step, a drawing step, and a heating step, and manufactures an alkali metal-doped optical fiber.
  • a silica glass-based optical fiber base material having a core containing an alkali metal having an average concentration of 0.5 atomic ppm or more is manufactured.
  • an optical fiber is produced by drawing an optical fiber preform in a drawing furnace.
  • the heating step the optical fiber is heated in a heating furnace provided between the outlet of the drawing furnace and a die for applying resin to the optical fiber.
  • FIG. 1 is a conceptual diagram of a thermal diffusion process in the optical fiber preform manufacturing process in the embodiment of the present invention.
  • a silica glass pipe 1 is prepared.
  • the silica glass pipe 1 contains 100 atomic ppm of Cl and 6,000 atomic ppm of fluorine, the concentration of other additives is below the detection limit (about 1 ppm), the outer diameter is 32 mm, the inner diameter Is 15 mm.
  • a handling glass pipe 5 is connected to one end of the glass pipe 1, a part of the handling glass pipe 5 is used as a raw material reservoir, and an alkali metal salt raw material (KBr) 3 is installed in the raw material reservoir.
  • a part of the glass pipe 1 may be used as a raw material reservoir.
  • the temperature of the outside of the raw material reservoir is increased by an external heat source (electric furnace) 2.
  • the state heated to 680 ° C. is maintained for 1 hour (drying step).
  • the alkali metal salt raw material 3 of the raw material reservoir is dried.
  • the temperature outside the raw material reservoir in the drying step is 270 ° C. or higher and lower than the melting point of the raw material alkali metal salt, preferably 800 ° C. or lower.
  • an external heat source oxyhydrogen burner is used so that the outer surface of the glass pipe 1 becomes 2000 ° C. ) 4 (heat diffusion step).
  • the oxyhydrogen burner is moved at a speed of 30 mm / min, and this is carried out 15 times in total, thereby diffusing potassium on the inner surface of the glass pipe 1.
  • the glass pipe 1 in which the alkali metal has been diffused is heated by the oxyhydrogen burner 4 so that the inner diameter is reduced to about 4 mm (reducing step).
  • the inner surface becomes about 5 mm in diameter by heating the glass pipe 1 to a temperature of 2000 ° C. with the oxyhydrogen burner 4 while supplying SF 6 and Cl 2 from the gas supply unit to the glass pipe 1.
  • Vapor phase etching of the inner surface of the glass pipe 1 is carried out (etching process).
  • the glass pipe 1 is heated to about 1400 ° C. with the oxyhydrogen burner 4 while evacuating the internal pressure in the pipe to about 100 kPa in absolute pressure. It implements and obtains the alkali metal addition glass rod whose outer diameter is about 25 mm (solidification process).
  • the outside of the glass rod is sufficiently ground until the OH group disappears (specifically, until the outer diameter becomes about 70% or less after the solidification), and this is the first core rod
  • a second core having a diameter that is about three times the diameter of the first core rod is provided outside the first core rod.
  • the second core is made of silica glass with an average of 6,000 ppm of Cl and other additives of 1 ppm or less.
  • the first core rod and the second core are combined to form a core portion, and further, silica glass containing fluorine serving as a first cladding portion is synthesized outside thereof.
  • the relative refractive index difference between the second core and the first cladding part (second core refractive index ⁇ first cladding part refractive index) / second core part refractive index is about 0.33% at maximum.
  • a silica glass containing fluorine having a relative refractive index difference with respect to the second core (second core refractive index ⁇ second cladding portion refractive index) / second core portion refractive index of about 0.23%. This is combined as the second cladding part and used as an optical fiber preform.
  • the core of the optical fiber preform contains an average of 1000 atomic ppm or more of alkali metal and chlorine, but does not substantially contain other transition metals such as Ge, Al, P, Fe, Ni, and Cu (0.5 atomic ppm). It is desirable that The core of the optical fiber preform may contain fluorine atoms. By doing so, it is possible to reduce the transmission loss of the optical fiber to 0.18 dB / km or less.
  • the core of the optical fiber preform preferably contains an alkali metal having a peak value of 500 atomic ppm or more. Transmission loss at a wavelength of 1550 nm of an optical fiber manufactured using this optical fiber preform can be reduced to 0.16 dB / km.
  • an optical fiber is produced by drawing this optical fiber preform.
  • This optical fiber has a core region containing an alkali metal (potassium) having an average concentration of 0.5 atomic ppm or more, and a cladding region surrounding the core region. Further, in the heating step, the optical fiber is heated in a heating furnace provided at the subsequent stage of the drawing furnace.
  • the heating furnace installed under the drawing furnace may be installed continuously with the drawing furnace.
  • the transmission loss of the optical fiber at a wavelength of 1550 nm is preferably as low as 0.160 dB / km or less, more preferably 0.155 dB / km or less, and further preferably 0.153 dB / km or less.
  • the effective area may be about 70 to 160 ⁇ m 2 at a wavelength of 1550 nm.
  • the chromatic dispersion at the wavelength of 1550 nm may be +15 to +22 ps / nm / km.
  • the zero dispersion wavelength may be 1250 nm or more and 1350 nm or less.
  • the dispersion slope may be +0.05 to +0.07 ps / nm 2 / km at a wavelength of 1550 nm.
  • the transmission loss at a wavelength of 1380 nm is preferably as low as 0.8 dB / km or less, more preferably 0.4 dB / km or less, and most preferably 0.3 dB / km or less.
  • the polarization mode dispersion in the wavelength 1550 nm band may be 0.2 ps / ⁇ km or less.
  • the cable cutoff wavelength is preferably 1530 nm or less, more preferably 1450 nm or less, which is a pump wavelength used for Raman amplification, and may be 1260 nm or less as in a standard single mode fiber.
  • the diameter of the core part is about 5 to 15 ⁇ m, and the relative refractive index difference between the core part and the cladding part (core part refractive index ⁇ cladding part refractive index) / core part refractive index is about 0.1 to 0.7%. is there.
  • the diameter of the outer periphery of the glass part in the optical fiber may be about 110 to 150 ⁇ m, and the diameter of the outer periphery of the optical fiber coated with resin is preferably about 200 to 300 ⁇ m.
  • Such an optical fiber is particularly preferably used as an optical transmission line in an optical transmission system for long-distance optical communication.
  • an optical fiber by drawing a silica glass-based optical fiber preform having a core containing an alkali metal having an average concentration of 0.5 atomic ppm or more, light extracted from a drawing furnace
  • a low-loss alkali-doped optical fiber with excellent hydrogen resistance characteristics that is, loss due to structural irregularities can be reduced
  • a high linear velocity that is, efficiency
  • the length of the heating furnace could be 5 m, which is a length that does not cause a problem in the drawing machine structure.
  • the drawing speed could be 150 m / min or more without significantly reducing productivity.
  • transmission loss can be further reduced.
  • the concentration of the alkali metal contained in the core of the optical fiber preform to 100 atomic ppm or less and setting the drawing speed and the heating furnace within a predetermined range, the hydrogen resistance characteristics of the optical fiber, particularly from the 1500 nm band, are gradually increased.
  • the new loss increase that gradually increases toward the long wavelength side is significantly improved compared to the optical fiber manufactured without a heating furnace. This is presumed that the number of point defects is reduced because the point defects existing in the manufactured alkali metal doped optical fiber are repaired by the relaxation of the glass network structure when the optical fiber passes through the heating furnace. Is done.
  • the optical fiber is previously exposed to deuterium (D 2 ) gas under a condition that (D 2 partial pressure) ⁇ (treatment time) is 50 kPa ⁇ hour or more at 20 ° C. or more (preferably 40 ° C. or more).
  • D 2 partial pressure deuterium
  • treatment time is 50 kPa ⁇ hour or more at 20 ° C. or more (preferably 40 ° C. or more).
  • the present inventors have suppressed transmission loss deterioration in the transmission band (wavelength 1300 nm to 1600 nm band, etc.) due to the alkali metal-doped optical fiber reacting with hydrogen, and further improved the hydrogen resistance characteristics. I found it.
  • the transmission loss at a wavelength of 1550 nm can be 0.158 dB / km, preferably 0.154 dB / km, and more preferably 0.152 dB / km or less.
  • the increase in transmission loss at a wavelength of 1550 nm after exposure to hydrogen can be 0.003 dB / km or less, preferably 0.002 dB / km or less.
  • the increase in transmission loss at 1520 to 1620 nm after hydrogen exposure can be 0.005 dB / km or less, preferably 0.003 dB / km.
  • FIG. 2 shows Examples 1 to 14
  • FIG. 3 shows Examples 15 to 28, and
  • FIG. 4 shows Examples of various optical fiber conditions (drawing speed, dwell time of the optical fiber in the heating furnace, heating furnace Temperature, the product of the furnace temperature and the residence time in the furnace, and the average cooling rate of the optical fiber in the furnace) and characteristics (transmission loss at a wavelength of 1550 nm, Rayleigh scattering coefficient, and structural irregularities) It is a chart summarizing (loss).
  • an optical fiber was manufactured by drawing a silica glass-based optical fiber preform having a core containing potassium having a concentration of 15 to 60 atomic ppm or more. The potassium concentration in the core of the manufactured optical fiber was 0.5 to 2 atomic ppm.
  • 42 conditions shown in FIGS. 2 to 4 were set.
  • the length of the heating furnace was 5 m.
  • FIG. 5 is a graph showing the relationship between the optical fiber residence time in the heating furnace, the heating furnace temperature, and the transmission loss of the optical fiber at a wavelength of 1550 nm for each of the optical fibers of Examples 1 to 42.
  • the horizontal axis represents the residence time of the optical fiber in the heating furnace, and the vertical axis represents the temperature of the heating furnace.
  • the temperature of the heating furnace is 700 ° C. or more and the product of the heating furnace temperature and the residence time is 480 ° C. or more, the transmission loss of the optical fiber at a wavelength of 1550 nm may be 0.158 dB / km or less. it can.
  • the temperature of the heating furnace is desirably 1000 ° C. or higher.
  • the furnace temperature is 1500 ° C in the current technology, but it may be possible to reach 2000 ° C in the future. In that case, it is possible to reduce the loss at a higher linear velocity.
  • the residence time of the optical fiber in the heating furnace is more preferably 0.3 seconds or more, and considering the productivity, the residence time of the optical fiber in the heating furnace is preferably 2 seconds or less.
  • FIG. 6 shows various conditions (drawing speed, residence time of the optical fiber in the heating furnace, temperature of the heating furnace, product of the heating furnace temperature and the residence time in the heating furnace) of each optical fiber of Comparative Examples 1 to 7.
  • 3 is a table summarizing the average cooling rate of the optical fiber in the heating furnace and various characteristics (transmission loss at a wavelength of 1550 nm, Rayleigh scattering coefficient and loss due to structural irregularities).
  • Each optical fiber of Comparative Examples 1 to 7 is a pure silica core optical fiber that does not contain an alkali metal in the core.
  • the temperature of the heating furnace was 1500 ° C.
  • the drawing speed was any one of the seven conditions shown in FIG.
  • the length of the heating furnace was 5 m.
  • FIG. 7 is a graph showing the relationship between the optical fiber residence time in the heating furnace and the transmission loss at a wavelength of 1550 nm for each of the optical fibers of Examples 1 to 7 and Comparative Examples 1 to 7.
  • the temperature of the heating furnace was 1500 ° C.
  • the residence time of the optical fiber in the heating furnace needs to be 1.0 seconds or more. .
  • the alkali metal-doped optical fiber of the example reduces the transmission loss by about 0.008 dB / km as compared with the pure silica core optical fiber of the comparative example. I can do this.
  • FIG. 8 is a table summarizing the increase in transmission loss for each of the optical fibers of Examples 1 to 7, 15 to 21, and FIG. 9 for each of the optical fibers of Examples 29 to 42 with or without deuterium treatment.
  • FIGS. 8 and 9 show the amount of increase in transmission loss at a wavelength of 1550 nm, the maximum value of increase in transmission loss at a wavelength of 1530 nm to 1570 nm, and the transmission loss at a wavelength of 1560 nm to 1620 nm in each case where deuterium treatment is performed.
  • the maximum value of the increase amount and the increase amount of transmission loss at the wavelength of 1380 nm are shown.
  • the transmission loss increase amount is an increase in transmission loss after hydrogen treatment relative to before hydrogen treatment. At any wavelength, the amount of increase in transmission loss was smaller in the optical fiber subjected to deuterium treatment.
  • the evaluation procedure of the transmission loss increase amount of the optical fiber regarding the presence or absence of deuterium treatment is as follows. (1) For each of Examples 1 to 7 and 15 to 21, two optical fibers each having a length of 2 km were prepared. (2) For each example, only one optical fiber was subjected to deuterium treatment at a deuterium gas partial pressure of 2 kPa, a temperature of 40 ° C., and a time of 24 hours. To remove hydrogen, it was left in the atmosphere at room temperature for over 2 weeks. (3) The transmission loss (initial transmission loss) of each of the two optical fibers in each example was measured. (4) Each of the two optical fibers in each example is left in an atmosphere containing hydrogen gas at a temperature of 25 ° C.
  • FIG. 10 shows the relationship between the residence time of the optical fiber in the heating furnace and the increase in transmission loss at the wavelength of 1550 nm for each optical fiber of Examples 1 to 7 with and without deuterium treatment. It is a graph which shows a relationship. Here, in the case where the deuterium treatment was performed and the heating by the heating furnace was not performed, the increase in transmission loss at a wavelength of 1550 nm was 0.0027 dB / km.
  • FIG. 11 shows the optical fiber residence time in the heating furnace and the increase in transmission loss at wavelengths of 1560 nm to 1620 nm for each optical fiber of Examples 1 to 7 with and without deuterium treatment. It is a graph which shows the relationship with the maximum value of. Here, in the case where the deuterium treatment was performed and the heating by the heating furnace was not performed, the maximum value of the increase in transmission loss at the wavelength of 1560 nm to 1620 nm was 0.0033 dB / km.
  • the increase in transmission loss due to hydrogen treatment can be reduced by heating the optical fiber after drawing in a heating furnace. It can be seen that when the residence time of the optical fiber in the heating furnace is short (less than 0.2 seconds), there is no effect, and the residence time of the optical fiber in the heating furnace is preferably 0.2 seconds or more.
  • an increase in transmission loss after hydrogen treatment can be reduced by about 0.001 dB / km in an optical fiber that has been subjected to deuterium treatment.
  • the increase in transmission loss at the wavelength of 1550 nm of the optical fiber can be reduced to 0.002 dB / km or less regardless of the residence time of the optical fiber in the heating furnace.
  • the increase in transmission loss at 1650 nm can be made 0.003 dB / km or less.
  • the increase in transmission loss at the wavelength of 1550 nm of the optical fiber is 0.003 dB / km or less, and the increase in transmission loss at the wavelength of 1560 nm to 1620 nm is 0.005 dB / km.
  • the residence time of the heating furnace may be set to 0.2 seconds or more. Further, by increasing the residence time of the optical fiber in the heating furnace, the increase in transmission loss of the optical fiber can be reduced regardless of the presence or absence of deuterium treatment.

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